your friend is right but it's advisable to diversify your protein sources because at the moment relying more than half of your daily protein intake on whey sounds unsustainable. i don't know about kidneys but most people have problems with whey because it has lactose. if you're not lactose-intolerant then you're good.

in bodybuilding everyone obsesses over proteins but actually you need to focus on other nutrients as well (dubbed the "macros"), primarily fats and carbs. the recommended ratio would be carbohydrates: 45-65% of calories, fat: 20-35% of calories, protein: 10-35% of calories. so i hope you don't neglect this.